1. Field of the Invention
The present invention relates to overhead exposure units and platemakers used for making photo reproductions in the graphic arts.
2. Background of the Prior Art
A variety of different overhead exposure units have been provided for making plates or other photographic reproductions on films and light sensitive sheet material. In general, film manufacturers recommend a light source to film distance of a certain value to provide optimum results in terms of uniformity of light distribution, light collimation requirements and exposure duration, etc. The distance recommendations may vary due to a number of factors such as exposure latitude of the film, size of the film to be exposed, number of overlays through which exposures are made, design of the exposure unit lamp and reflector system.
Some graphic art equipment manufacturers provide exposure units which adjust the distance between the light source and film by moving the light source closer to or further away from the film which is generally held in a vacuum frame on a stationary table or the like. In many instances, it is normal to recommend a minimum light source to film distance of 72 inches and considering that many graphic art studios are located in conventional rooms having a nominal eight foot high ceiling, it has been difficult to provide an overhead exposure unit which would accommodate a light source to film distance of 72 inches. Moreover, it is desirable for speed of reproduction to have a support table and vacuum frame at a convenient working level of approximately 36 inches above the floor on which the operator is standing. Assuming that approximately 12 inches may be required from the lamp to the ceiling in an eight foot high room ceiling, it has been difficult to provide an overhead exposure unit with both a light source to film distance of 72 inches and a table mounted at a convenient working level of about 3 feet above the floor.